<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>

  </style>
</head>
<body>
<input type="text"/>
<script>
  var input = document.querySelector('input');
  document.addEventListener('keyup', function (e) {
    if (e.keyCode === 83) {
      input.focus();
    }
  })
</script>

</body>
</html>